Steel concentrically braced frames are generally designed to resist lateral force by means of truss action. Columns are designed for axial force and column moment demands are often ignored. However, if the columns cannot carry moment, a soft-story mechanism may occur, causing large concentrated deformations in only one story. Such large concentrations of damage are not generally seen in real frames where columns are continuous and possess flexural stiffness and strength. This paper develops relationships for between column stiffness and drift concentration for a two-story frame based on push and dynamic analyses. It is shown that the presence of continuous columns in a structure significantly decreases the possibility of large drift concentrations.
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